Incendiary capture device

ABSTRACT

A method and apparatus is provided for catching and extinguishing burning particles so that they may be retrieved for study. A receptacle filled with inert powder is placed within the realm of falling particles and the inert powder fluidized, for example, by sublimating cubes of dry ice placed under the powder.

United State s Patent [191 Smith 1451 Dec; 17, 1974 [5 INCENDIARY CAPTURE DEVICE 3,793,101 2/1974 Mullarkey 23/230 1 c x [75] Inventor: Warren K. Smith, Poway, Calif; FOREIGN PATENTS OR APPLICATIONS 73 Assignee; The United States of America as 579,473 7/1959 Canada 73/l67 represented by the Secretary of the I Navy, Washington, DC. Primary Examiner'Richard C. Queisser Assistant Examiner]oseph W. Roskos- V [22] Flled Sept 1973 Att0rney,.Agent, o'r Firm-R. S. Sciascia; Roy Miller; [21] Appl. No.: 400,449 Gerald F. Baker 52 us. Cl. 73/167 [57] ABSTRACT V [51] Int. Cl. GOln 33/22 A method n pp ra is pro i ed for catching and [58] Field of Search 73/167, 28, 35, 432 R; x ingu hing rning p r icles s hat theymay be re- 23/230 PC trieved for study. A receptacle filled with inert powder is placed within the realm of falling particles and the [56] Refer nces Cit d inert powder fluidized, for example, by sublimating UNITED STATES PATENTS cubes of dry ice placed under the powder.

3,475,965 11/1969 Koblin et al. 73/28 10 Claims, 3 Drawing Figures PATENTEL; can 1 7 I974 sum 1 or 5 Fig. I

PATEHTEL SUI] H974 sum 2 0F 5 ARROW PENETRATION, CM

Fig. 2

PATENTEU HEB] 7 i974 sum 3 or '5 ARROW PENETRATION, CM

Fig. 3

INCENDIARY CAPTURE DEVICE BACKGROUND OF THE INVENTION from surface combustion during their trajectory. Upon impact, the hot particles or droplets spatter into much smaller pieces, which are either lost or completely burned up before recovery. It is then practically impossible to study the size distribution and character of the particles so that this can be related to target damage potential.

Considerable effort has been made in the past to find a suitable medium to capture burning white phosphorus particles from shells and grenades. Various detergent solutions, foams, and soft fibrous beds were tried without success. It is also necessary to quench and prevent further burning immediately upon capture, and this requirement may have prevented successful employment of some of the candidate media. Some success has been reported with an indirect method consisting of catching the white phosphorus particles on wet sand. The particles spatter upon impact, of course, producing star-burst patterns on the wet sand. It is, therefore, necessary to have a calibration of star-burst size versus known white phosphorus particle sizes in order to evaulate the star-bursts obtained from this method. However, no knowledge was gained in such tests as to particle shape and condition or what proportion was yet unburned. H

In addition to the requirements of softness of the recovery bed, practically zero surface tension, ability to cool the incendiary particle rapidly and prevent further oxidation, there is also the necessity for a low-cost and simple system. As. many as 24 catching devices may be arrayed around the shell burst point. These must be serviced and the product removed rapidly after each test.

According to the present, invention, incendiary particles are captured in a fluidized bed of inert nonwettable powder. The powder is fluidized by placing readily obtainable dry ice under the powder in sufficientquantity to keep the bed of power fluidized by the gas produced by sublimation of the dry ice. The apparent density of the fluidized. bed can be adjusted by regulating the quantity and'block size of the dry ice used and incendiary particles are easily recoverable from the device.

BRIEF DESCRIPTION OF THE sEvERALvIEws OF THE DRAWING the container 11 is hung a basket l2 by means of han-' supports a screen bottom 14 with mesh fine enough to retain the smallest particle practically useful to retrieve. In this instance layers of chunks of dry ice 15 are shown in the bottom of the container and a second layer of dry ice in the basket. The remainer of the space in the container is nearlyv filled with a non-wettable inert powder 16. 'In the device shown in FIG. 1, the powder is indicated as being essentially potassium bi carbonate KHCO although any of a number of inert powders may be used. It is also desirable that the powder be insoluble and non-wettable.

A conveniently available and highly suitable powder was found to be a fire extinguisher powder consisting of KHCO finely ground and treatedwith a silicone compound 'tomake it insoluble and .non-wettable. This powder popularly known as PurpleK is a US. Government stock item supplied by Chemical Concentrates Corporation, Fort Washington, PA, .to MlLF--22 2- 87A* in 50 lb. steel buckets. These buckets were found to make excellent containers for the purposes of this invention. 92 percent'by weight KHCO; 0.2 max moisture; remainder silicone waterproofing and anti-caking ingredients.

This arrangement provides a soft cool extinguishing bed of fluidized powder to catch incendiary particles for study. v

ANALYSIS In the beginning it was established as general guidelines that particle sizes of one-eighth, one-fourth and one-half ml by volume were to be expected and that they might have fallen from a maximum height of 100 ft. From-this the maximum energy to be absorbed by a capture medium was calculated by the following procedure:

The kinetic energy of the falling WP particle is given by and in turn the velocity, v, at the'end of 100-ft fall is given by where V terminal velocity S= cross-sectional area of the particle At terminal velocity, weight drag, hence where p =Iair density, slug/ft r C drag. coefi'icient, 0.47

I Fluid-Dynamic Drag," by S. F. Hoemcr. I965, pp. 3-8'.

dles l3 resting on the upper rim. The basket frame 12 KE /2 0.00203/32.2 x (58.4) a 0.1071 ft-lb.

This kinetic energy must be absorbed within a reasonable depth of penetration into the capture medium. The next step, therefore, is to measure the energy absorption by penetration. For this purpose the incendiary particles were simulated by arrows in which the tips were styrofoam balls of one-eighth, one-fourth, or onehalf ml volume, the shafts were balsa wood, and instead of feathers, paper fins were used at the rear for stability. The shafts and fins were tailored so that the total weight of the arrows divided by the volume of the styrofoam balls gave an apparent density equal to that of solid white phosphorusnamely, about 1.85. A notch was cut at the back of each shaft so that gram weights could be hung by fine threads for the static penetration tests.

The penetration data were obtained by noting the depth of penetration for various loads on the arrow. By measuring the area under the resulting curves of penetration depth versus load and replotting it as energy absorbed versus penetration depth, one can then readily determine penetration. depth for any kinetic energy. The use of such an arrow for these tests made it convenient to measure penetration into an opaque medium.

Five pounds of dry ice in blocks averaging about 2 X 3 X 1 inches were placed in the bottom of a'Purple K bucket, evenly scattered, and 45 pounds of Purple K powder were slowly shoveled on top of the dry ice. The apparent volume increased about 25 percent due to the boiling or fluidizing action. Gram weights were hung on two arrows, one with a /z-ml cube and the other with a Vz-ml sphere of styrofoam, to obtain load versus penetration curves as'shown in FIG. 2. These were replotted as energy absorbed (area under the curves) versus penetration (FIG. 3). As noted earlier, a value of 0.1071 ft-lb or 1,480 g-cm was obtained fora /2-ml particle falling 100 ft. This exceeds the range of the curves of FIG. 2, but an extrapolation gives a penetration depth of 34 cm or 13.4 inches, therefore, the -inch-deep bucket of Purple K would be sufficient.

A drop penetration test was made to check the validity of these calculations. It was difficult to arrange al00-ft drop test, so the drops were made from a height of 11.2 ft, for which it was calculated the z-ml cube should penetrate 7.5 inches. A total of 6 drops were made, averaging 7.2 inches penetration, which was considered a reasonably good check.

CONCLUSION This capture device avoids the thermal shock of liqv uid-quenching of burning particles and also the forces of surface impact. It also provides a protective medium until retrieval. A fluidized bed is produced without r'esort to mechanical pumps or cylinders or compressed gas; the apparatus is extremely simple and inexpensive.

The fluidized bed can be produced by piping in any other desired inert gas, or by using other frozen gases which vaporized directly from the solid. Any other suitable inert powder compatible with the incendiary materials may be used.

Particles caught in the beds of powderare retrieved by lifting the basket and washing away any powder clinging to the particles. Maintaining some dry ice on the screen aids in moving the basket through the powder and fluidization maybe continued indefinitelyby addition of dry ice above and below the screen while tests are being conducted.

The non-wettable property of the Purple K powder used makes it easy to flush the powder away from the retrieved particles.

What is claimed is: l. A method of investigating the effectiveness of incendiar'y weapons including: placing a plurality of containers in spaced relationship in an area surrounding a weapon to be tested;

creating a fluidized bed of inert powder in each container; activating the test weapon; and

examining any incendiary particles falling into said a quantity of inert nonwettable powder in said container; means associated with said container for causing said powder to assume a state of fluidization; and means for separating and removing from said powder particles of incendiary matter entering said container.

7. Apparatus according to claim 6 wherein said powder consists essentially of potassium bicarbonate.

8.. Apparatus according to claim 6 wherein said means for fluidization comprises solidified carbon dioxide.

9. Apparatus according to claim 6 including a basket fitted in said container and having a metal'screen bottom and handles extending outside said container.

'10. Apparatus according to claim 6 wherein said powder consists essentially of potassium bicarbonate treated to be nonwettable;

said means for fluidization comprises solidified carbon dioxide; and 3 a basket fitted in said container-and having a metal screen bottom and handles extending outside said container. 

1. A method of investigating the effectiveness of incendiary weapons including: placing a plurality of containers in spaced relationship in an area surrounding a weapon to be tested; creating a fluidized bed of inert powder in each container; activating the test weapon; and examining any incendiary particles falling into said fluidized beds.
 2. The method of claim 1 wherein said powder is treated to be non-wettable.
 3. The method of claim 1 wherein the powder comprises potassium bicarbonate treated to be non-wettable.
 4. The method of claim 3 wherein said powder is fluidized by sublimation of solidified carbon dioxide.
 5. The method of claim 1 wherein said powder is fluidized by sublimation of solidified carbon dioxide.
 6. Apparatus for catching and retrieving incendiary particles comprising: a container; a quantity of inert non-wettable powder in said container; means associated with said container for causing said powder to assume a state of fluidization; and means for separating and removing from said powder particles of incendiary matter entering said container.
 7. Apparatus according to claim 6 wherein said powder consists essentially of potassium bicarbonate.
 8. Apparatus according to claim 6 wherein said means for fluidization comprises solidified carbon dioxide.
 9. Apparatus according to claim 6 including a basket fitted in said cOntainer and having a metal screen bottom and handles extending outside said container.
 10. Apparatus according to claim 6 wherein said powder consists essentially of potassium bicarbonate treated to be nonwettable; said means for fluidization comprises solidified carbon dioxide; and a basket fitted in said container and having a metal screen bottom and handles extending outside said container. 